Motorcycle: Racers - KR/ KRTT 1952 - 1969
Date: Sunday, October 31 @ 15:24:46 UTC
Topic: Motorcycle, Motorcycles, Motor Cycle
KR/ KRTT 1952 - 1969
What Harley-Davidson needed to replace the elderly WR was a machine reflecting the technology of its era. In the KR, the company most certainly didn't get it. What it got instead was yet another long-stroke flathead racer derived from a road bike, in this case the 45.3cu in (742cc) Model K which was about to be so comprehensively licked by British machines on America's streets. In racing, the KR had an edge: the AMA's 500cc limit on overhead-valve engines still applied.
As with the WR a decade earlier, production began slowly, with just 17 KRs built in the first year. Yet by 1955, the special equipment range encompassed no less than five specific models: the KHK Super Sport Solo, KHRM off-roader, KR dirt track racer, and KRTT and KHRTT "Tourist Trophy" machines.
All three KH models boasted the new 55cu in (883cc) long-stroke K-Series engine and were essentially "race replicas" intended as much for the private enthusiast as the racer. Serious racers remained limited to what the regulations allowed: 750cc.
In 1955, the factory built 90 45-inch competition models, declining to 33 by the decade's end. Unlike the WR/WRTT, all variants now enjoyed a lightweight racing frame, although only the road-racing TT model received the new swinging-arm rear end. The flat-track KR had a smaller tank, fatter wheels and tyres and no need of brakes. Bore and stroke were identical to the WR's at 70 x 97mm (the slow-revving 55's stroke was even longer at 116mm).
However, the cylinders were commonly re-bored after bedding-in. By using the maximum permitted piston oversize — more than 0.04in (1.1mm) mechanics could raise the displacement legally to 46.8cu in (767cc).
At 9:1, the compression ratio was high by side-valve standards and a single 33mm Linker! carburettor was standard. Power was around 48bhp at 7000 rpm, with 501b/ft (68Nm) of torque at 5,000rpm. British Norton, Matchless and Triumph machines, as well as putting out far more specific
power than the KR, handled and stopped far better. Yet the old KRs just kept rolling on.
Wile they were heavy (around 380 lbs/172kg) and ill-suited to any circuit with proper corners, they remined surprisingly competitive elsewhere — not least because everyrace grid in America seemed to be packed with them.
Since a dirt-track KR actually cost
$95 less than a stock road-going Sportster during the mid-1960s, perhaps this wasn't too surprising. The road racers, too, were capable of surprising feats. At the super-fast Daytona Speedway, streamlined KRs have been recorded in excess of 150mph (240kph), an astonishing achievement for a side-valve machine. For all their shortcomings, in the hands of racing aces such as Markel and Resweber, they managed to win a round dozen American national titles during their 18 years on the grid. The KR's astonishing span came to an end in 1969 when the AMA ended discriminatory limitations on overseas machines. Faced with a level playing field, there was no way that the redoubtable old flathead "45" could compete with the machines that were coming in from abroad.
Engine: side-valve 4-stroke V-twin
Capacity: 45.3 cu in (742cc)
Weight: 377-3851bs (171-175g)
Wheelbase: 56in (1,420mm)
Top speed: 150mph (240kph) (with road-race streamlining)
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